Electrochemical cells have recently been actively studied. Among electrochemical cells, for example, because a polymer electrolyte electrolysis cell (PEMEC) is superior in responsivity to renewable energy such as photovoltaic generation, the PEMEC is expected to be used for generating hydrogen for a large scale energy storage system. Platinum nanoparticle catalyst and particulate iridium series catalyst have been typically used for the negative electrode and the positive electrode of the PEMEC, respectively, to secure sufficient durability and electrolytic performance.
One major issue to spread the PEMEC is cost reduction by reducing the amount of noble metal catalyst to be used.
Carrierless catalyst units having a porous structure or a laminated structure including a void layer have recently been proposed as a noble metal catalyst for an electrochemical cell. The configuration of the catalyst included in the catalyst units is in a sponge-like state or a nanosheet-like state, and it has been reported that the catalyst units have high durability. Furthermore, because porosity of the catalyst layer including the catalyst units is high, the catalyst layer is advantageous in material motion indispensable for electrode reaction of electrochemical cell, and is probably a leading technique for reducing the amount of noble metal. However, when the above technique is applied to a PEMEC, stability of water electrolysis performance is still insufficient, so that further improvement is needed.